3com 5500-ei pwr Instrução De Instalação

 

2-2 

telephone users (in VLAN 201 to VLAN 300). Packets of all these users are forwarded by Switch A to 

the public network.  

After the selective QinQ feature and the inner-to-outer tag mapping feature are enabled on the port 

connecting Switch A to these users, the port will add different outer VLAN tags to the packets according 

to their inner VLAN tags. For example, you can configure to add the tag of VLAN 1002 to the packets of 

IP telephone users in VLAN 201 to VLAN 300 and forward the packets to the VoIP device, which is 

responsible for processing IP telephone services.  

To guarantee the quality of voice packet transmission, you can configure QoS policies in the public 

network to reserve bandwidth for packets of VLAN 1002 and forward them preferentially.  

In this way, you can configure different forwarding policies for data of different type of users, thus 

improving the flexibility of network management. On the other hand, network resources are well utilized, 

and users of the same type are also isolated by their inner VLAN tags. This helps to improve network 

security.  

Like the VLAN-VPN feature, a port with the selective QinQ enabled adds the source MAC addresses of 

user packets to the MAC address table of the default VLAN on the port. However, the port with selective 

QinQ enabled can insert an outer VLAN tag other than that of the default VLAN to the packets. Thus, 

when packets are forwarded from the service provider to users, they may be broadcast if their 

destination MAC addresses cannot be found in the MAC address table of the outer VLANs.  

Figure 2-2 Learn MAC addresses of selective QinQ packets 

VLAN3
MAC-A

VLAN4
MAC-A

PVID=2

Private 

Network

Public 

Network

Private 

Network

Public 

Network

PVID=2

VLAN4
MAC-A

Receives the data that the 
private network sends to the 
service provider’s network

Receives the data that the 
service provider’s network 
sends to the private network

 

 

As shown in 

, the default VLAN of the port used to receive packets is VLAN 2. The port is configured to 

receive packets of VLAN 3, tag the received packets with the outer tag of VLAN 4, and add the source 

MAC addresses (MAC-A) of the packets to the MAC address table of its default VLAN (VLAN 2).  

When a response packet is returned to the device from VLAN 4 of the service provider network, the 

device searches the outbound port for MAC-A in the MAC address table of VLAN 4. However, because 

the corresponding entry is not added to the MAC address table of VLAN 4, this packet is considered to 

be a unicast packet with unknown destination MAC address. As a result, this packet will be broadcast to 

all the ports in VLAN 4, which wastes the network resources and incurs potential security risks.  

The Switch 5500-EI series Ethernet switches provide the inter-VLAN MAC address replicating feature, 

which can replicate the entries in the MAC address table of the default VLAN to that of the VLAN 

corresponding to the outer tag. With the inter-VLAN MAC address replicating feature enabled, when a 

device receives a packet from the service provider network, this device will find the path for the packet 

by searching the MAC address table of the VLAN corresponding to the outer tag and unicast the packet. 

Thus, packet broadcast is reduced in selective QinQ applications.